This invention relates generally to semiconductor laser devices for producing laser light and, more particularly, to a divided electrode type semiconductor laser device designed to facilitate and improve the separation of the electrodes.
FIG. 2 shows the structure of a lateral junction type buried semiconductor laser device.
This laser device includes a double-hetero-structure which is formed on a semi-insulating substrate 131 and in which a GaAs active layer 137 is interposed between undoped AlGaAs clad layers 133 and 135. For carrier injection, a p-AlGaAs clad layer 139, a p-GaAs cap layer 140, an n-AlGaAs clad layer 141 and an n-GaAs cap layer 142 are formed and buried on the left-hand and right-hand sides of the GaAs active layer 137 respectively as viewed in FIG. 2, and electrodes 143 and 145 are formed on these layers.
In the thus-constructed laser device, a current flowing through the electrodes 143 and 145 is confined between the undoped AlGaAs clad layers 133 and 135 having a high resistance, and carriers are thereby injected into the GaAs active layer 137 having a smaller energy band gap, so that light is generated by recombination of electrons and holes. The generated light is confined between and guided by the upper and lower, left and right clad layers, thereby emitting laser light in the direction perpendicular to the plane of projection of FIG. 2. This laser device is specifically suitable for integration because of the construction in which the device is constructed on the semi-insulating substrate 131, the carrier injection clad layers are positioned on the opposite sides, and the electrodes are independent of the substrate.
FIG. 3 is a top view of the semiconductor laser device shown in FIG. 2. As shown in FIG. 3, leads 147 and 149 are connected to the electrodes 143 and 145, a current is supplied through these leads to inject carriers from the buried carrier injection layers 111 and 113 into the active layer, thereby emitting laser light from opposite ends of the device.
This lateral-junction buried semiconductor laser device may be divided into a plurality of elements which are independently used for oscillation, control and so on to effect pulse oscillation or the like by controlling laser oscillation. For the manufacture of such a tandem electrode type laser, it is necessary to divide each electrode of the semiconductor laser device into a plurality of elements. Conventionally, the electrodes are divided in such a manner that, as shown in FIG. 4, the carrier injection clad layer and the electrodes are partially removed by gas-phase or liquid-phase etching using HCl gas or H.sub.2 O.sub.2 to form grooves 151 which separate the electrode 143 into electrodes 143a and 143b and the electrode 145 into electrodes 145a and 145b.
However, in a case where a lateral junction type buried semiconductor laser has electrodes divided by etching in this way, the active layer into which electrons and holes are injected from the left and right clad layers has a small thickness of about 0.2 .mu.m and a large width of about 2 .mu.m, and the forward-direction resistance tends to increase. It is therefore necessary to increase the amount of doping for the n-type and p-type clad layers and to form n-type and p-type GaAs cap layers for reducing the resistance of contact with the electrodes. To satisfy these requirements, the facility with which the electrodes are separated as shown in FIG. 4 is sacrificed.
To improve the separation based on etching, it is necessary to etch the outer layers to a depth very close to the active layer. A portion of the active layer may be removed if the extent of etching is excessive, or the electrode cannot be suitably separated if the extent of etching is insufficient. The process of separating the electrodes is thus difficult.